The toner pump is described in U.S. Pat. No. 5,012,289 to Aldrich et al. It is a device which meters toner from a chamber above the developer station. The developer station employs a toner adding roller, which is at a predetermined electrical potential higher than that of the developer roller. The toner adding roller rotates in a bed of toner in contact with the developer roller and thereby applies toner onto tile surface of the developer roller charged primarily to the same electrical sign as that of both the toner adding roller and the developer roller. The developer roller then rotates past a doctor blade which is charged to a potential higher than the developer roller and rejects much toner having the other potential (termed wrong sign toner). Such a system does not operate reliably under the pressures of a high column of toner which can reach the doctor blade-developer roller nip. The toner pump is employed to limit the toner head reaching the doctor blade-developer roller nip.
Elimination of the toner pump reduces manufacturing and material cost and unwanted pressure variations during operation caused by the operation of the pump, which have been remedied by a vent between both sides of the toner pump and by close tolerances. A two phase toner pump has also been developed to remedy this effect and is the subject of U.S. Pat. No. 5,101,237 to Molloy.
Elimination of the toner pump reduces variations in torques, since the other rollers are driven off the same power source as the toner pump. Reduction in such fluctuations can reduce jitter or, alternatively, reduces costs in powering the system adequately to avoid jitter.
U.S. Pat. No. 5,086,728 to Kinoshita shows a toner applying roller horizontal to a developer roller, but is not otherwise closely similar to this invention.